Figure 4.

Brain and plasma (P) E₂ content in adult male zebra finches (n = 12) using the optimized combined liquid–solid-phase extraction procedure. Elevated brain E₂ content demonstrated here corresponds to functional and region-specific differences in aromatase (ARO) and estrogen receptor (ER) expression in the zebra finch brain. Plus signs indicate elevated expression of ARO and ER for each brain region; minus signs indicate little to no expression (after Shen et al., 1995; Metzdorf et al., 1999; Saldanha et al., 2000). Abbreviations as in Figure 1. P, plasma. Letters indicate significant differences among brain regions (p < 0.05).